Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.67   8.534%   $224.3072   $224.31   $224.30   $224.30  
  Purchase #2 $191.82   5.487%   $202.3452   $202.35   $202.35   $202.30  
  Purchase #3 $98.47   11.175%   $109.474   $109.47   $109.45   $109.50  
  Purchase #4 $206.45   8.497%   $223.9921   $223.99   $224.00   $224.00  
  Purchase #5 $109.61   5.297%   $115.416   $115.42   $115.40   $115.40  
  Purchase #6 $20.51   3.173%   $21.1608   $21.16   $21.15   $21.20  
  Purchase #7 $59.82   8.357%   $64.8192   $64.82   $64.80   $64.80  
  7 purchase totals = $893.35       $961.5145   $961.52   $961.45   $961.50